Electron beam apparatus



9, 1960 M. CHODOROW ELECTRON BEAM APPARATUS Filed Jan. 14, 1954 fIIEI l2 2 //A r W 7 w e m v FIFE-:3:-

IN VEN TOR. MARI Ml .CHODOEOW ELECTRON BEAM APPARATUS Marvin Chodorow,Menlo Park, Calif.,-assignor to Varian Associates, a corporation ofCalifornia Application January 14, 1954, Serial No. 404,040 Claims.(Cl.315-3.5)

This invention relates in general to electron beam dischargeapparatusand methods and, more particularly, to

novel devices of the slow wave type such as, for example,

of interdigital fins are maintained at difierent relative values ofpotential.

Another object of the present invention is to provide anovel electronbeam device having a slow wave structure which electrostatically focusesthe beam, whereby the use of permanent or electromagnets for focusing iseither unnecessary or the amount of magnetic field required for focusingis substantially reduced.

1 Still another object of the present invention is to pro- .vide a noveldevice of the above character having a slow wave structure ofthevinterdigital type wherein one set of interdigital fins isstructurally difierent from the associated second set of fins tocompensate for the alternate changes in beam velocity due to the beamfocusing electric field components parallel to the electron beam whichare directed in alternately opposite directions between successive pairsof fins.

These and other objects and advantages of the present invention will bemore apparent after a perusal of the followingspecification taken inconnection with the accompanying drawings, wherein Fig. 1 is alongitudinal sectional view of an electron beam device illustrated as atraveling wave tube amplifier of the interdigital ffin type constructionwherein the electron beam passing through the tube is electrostaticallyfocused,

,Fig. 2 is a cross-section view of the traveling wave tube amplifiertaken along section line 22 in Fig. 1,

Fig. 3 is a diagrammatic view showing the electric field lines betweensuccessive pairs of the interdigital fins of the traveling waveamplifier device shown in Fig. 1, and Fig. 4 is a diagrammatic sectionview of an embodiment of the pesent invention wherein alternate fins inthe interdigital structure are of a different configuration than thefins in the remaining set of interdigital fins to compensate forvelocity changes in the beam due to the electric field lines. i

Referring now to Figs. 1 and 2, the traveling wave tube amplifie riwhichembodies the novel interdigital structure ."ofithis invention comprisesa main body portion 1 of substantially an elongated U-shapeconfiguration and a top portion 2 alsoof Ushape cross section which isadapted tofitonto the main body portion 1 and form the hollow elongatedtubebody, these bodies being of a good con- United States Patent 0 iceducting metal such as copper or plated with a good conducting metal.Mounted on the right-hand end of the body is a collector assembly whichcomprises a metallic electron collector 3, an end adapter 4 and aninsulating seal 5 as of glass. Secured on the left-hand end of the tubebody is a cathode assembly which comprises the gun anode 6, the cathodegun assembly 7 including the cathode button 7', and the insulatingmounting seal 3 as of glass.

Secured on the main body portion 1 and extending upwardly within thetube body are a plurality of equally spaced metallic fins or loadingmembers 9. Mounted within the tube body is a substantially U-shapedelongated member or plate 11, the plate being mounted on the main body 1and insulated therefrom by insulating spacers 12. The plate 11 is spacedfrom the wall '2 of the body and electrically insulated therefrom bysuitable spacers 13 as of ceramic. Mounted on this plate 11 andextending downwardly within the tube are a plurality of equally spacedfins or loading members 14, these fins 14 being so arranged as to form auniform interdigital structure with the fins 9 along the length of thetube. A small aperture 15 is located in each of the fins 9 and 14, theseapertures being in axial alignment with the cathode button 7 and thecollector 3 so that a clearpath is provided for the electron beam fromthe cathode through the interdigital structure to the collector. Asubstantially L-shaped member 16 is provided on either side of the tubefor utilization as a choke.

An input waveguide 17 having an associated window seal 18 is coupledthrough an aperture in the body portion 1 to the space between the firstset of fins 9 and 14 on the left-hand side in Fig. 1. An outputwaveguide 19 with its associated window seal 21 is coupled through asecond aperture in the main body portion 1 to the space between thefurthermost set of fins 9 and 14 on the righthand side of the tube. Thecathode is connected to a source of potential 22 which places thecathode at a negative potential with respect to the main body of thetube and the collector 3. The insulated plate '11 and associated fins 14are connected to a source of potential 23 which maintains this plate andfin assembly at a positive potential with respect to the main bodyportion 1 and associated fins 9.

In operation, a stream of electrons, shown in dot-dash lines in Fig. 1,is emitted from the cathode button 7 and is accelerated by the positivevoltage on the gun anode, the stream of electrons being focused into abeam while passing through the aperture in the gun anode 6. The beam ofelectrons proceeds along the path defined by the apertures 15 in theinterdigital structure. The expended beam of electrons is then collectedby the positively charged collector electrode 3. The wave energy to beamplified is transmitted into this traveling wave amplifier through theinput waveguide 17, the wave energy traveling in a sinuous path alongthe interdigital structure defined by the fins 9 and 14 such that thewave travels along the tube at the same velocity as the electron beam ina well-known manner and extracts energy from the beam. The amplifiedwave energy is extracted from this traveling wave tube through theoutput waveguide 19.

This novel construction of a. slow wave tube is utilized in cooperationwith selected electric potentials to electrostatically focus theelectron beam so that the beam retains its small cross-section as itproceeds along the length of the tube, thus eliminating the necessityfor a magnetic field focusing means such as a permanent magnet orelectromagnetic coils. As stated above, the plate 11 and fins 14 are ata potential positive with respect to the niain body portion 1 and fins 9and thus an electric field is produced between the fins 9 and the fins14. The electric field pattern set up between the interdigital finswhichwould produce the optimum electron beam focusing is shown in partinFig.3"by the arrowe'd' lines. "The electric field lines are shown in thedirection of electron deflection. In the absence of the apertures, theelectric field lines"between"thef'fins Wouldbeparallel withthe' axis ofthe beam and essentially constant across the position of the apertures.With the apertures present the electric field pattern in the beampathhasboth longitudinal .and circularly symmetric radial components ofelect-ric'field. The'longitudina'l component causes 'the velocity of theelectrons in the axial direction to vary. "When theelectron'velocity issmaller than the average, the radial component of electric fieldproduces an inward force, and when the velocity is larger, theradialelectriefielfd produces an outward force. Because o flthe velocityva'riatio'n, however,' the electrons spend more time in the region ofinward force and -hence acquire a, net inward momentumfrom thefocusingffield. This canlbe used -to"balance"'the outward momentumldueto electronicpulsion forces which co'ntinually act within the beam, andwould. cause the beam 'toldiverge if no'focusing forces were. present.

One other effect Which may, in somelrinstances ermilization'ofthe novelelectrostatic focusing schemeflgive riseto undesired operation'is that.Ithe electric,.field" between one interdigital 'fin9an'd itsimmediately preceding associated fin14 is'in .one particulardirectionwhile the electric field' between "the same interdig-ital'fin 9and '-the immediately succeeding interdigital fin 1'4isinthejopposite'direction. Thus the'first mentionedfieldis' in'the'di-re'ction which opposes theielectron flow while theother field is inthe direction which; aids: the electrontfiow and therefore the velocity'ofithe electrons asthey enter -any one interdigital'lfin 9 is less thanthe velocity when they enter the succeeding interdigit'a-l'fin' 14.Thus, the transit angle through the 'fins 9 is greater than theitransitangle through the fins 14, the cumulative e'ifect of which "may besufficient to destroythe. required;phase relationship With theradio-frequencytwave To remedythis 'eifectthe novel structure shown in'Fig."4" maybeutilized Where the thickness ofv the fins 14 is greater.than-thethickness of"thefins"9 sothat the transit 'angles'throughthe-"fins '9'and' 14 maybe made equal.

interpreted as illustrativeand not in a limiting sense.

What is claimed is:

1. A slow-wave electron beam device of the-type wherein anelectromagnetic wave is made to -travel through"-the"device' coupledto'and substantially at'the velocity of an electronbeam thereintsu'chthat an energy exchange occursbetween' the beam" andthe-Wave comprisingmeans 'for producing a beam of electronsdirected through said device, a-'slow-'wave"structure associated with the'beampath comprising aninterdigital structure having a first plurality of loading memberselectrically coupledtogether and a second plurality'of loadingmemberselectrically coupled together, said'loa'ding members {havingapertures'therein aligned with-the beam patln'said loading members"being" interdigitally' ;space'fcl*along the beam path'"whereby asinuous wave-energy path is formed defined by the loading members forthe transmission' of said electromagnetic wave 'in a-sinuouspath-directed along and coupled to saidbeam; means'electricallyinsulating said first pluralityof'loadingymernbers from said secondplurality, Land means for applying-"different 'direct current electricalpotentials to said-two'pluralities of loading m'emb'erssuch' thatelectrostatic focusing fields extend between adjacent -loadi-ngmeI'n-bers at the; beam ipath apertures'forfocusingthe b'eam.

s same 2. A slow-wave electron beam device of the type wherein anelectromagnetic wave is made to travel through the device coupled to andsubstantially at the velocity of an electron beam therein such that anenergy exchange occurs between the beam and the wave comprising meansfor producing a beam of electrons, a base member having a plurality ,o fequally spaced loading members mounted thereonand'extending inwardlyinto the oatemplatezposinonedimms ssddz her in apl a ity. o 51 l r pac dst s sts mounted thereonandeiitendin toward thefbase member, saidlatterloading members be'ing in -interdigital relationp tsaii ten-n teasn members tal jih tth a sinuous wave-energy path isjform ed throughthe'device defined by the loading--member"s', s'aid loading members eachhaving an aperture therein, the apertures being aligned within thedevice so as to be aligned with the electron beam path therethrough suchthat the electron beam {is coupled to the electromagnetic-wave passingalong "the W sinuous pa-th for' energy exchange, means -for mountingsaid top plateon said" base member including insulation {electricallyinsulating the top plate trom the base member, and[-means-=-for applyingdifferent direct current electricalpotentials to said base and top platewherebyan electrostatic focusing field-may extend betweenadjacentloading members at the beam -path apertures.

' 3. A'slow-wave elect-ron beam device-ofthe type-whereinanelectromagnetic wave is made to travel through-eke device; coupled--to--and; substantially at the-.velocity of an electron beamthereinsueh th'atan energy exchange occurs between the beamand thewave-eomprisingmeans for producing a-beam-of-electrons=dire'cted;-through' said de- Vice, a slow-wave structureassociated withfth'e beampath comprising a first plurality of loadingmembers electrically coupled together and a secpnd;p1urality of-leadingmembers electrically coupled togethen -the-members;of the twopluralities; being alternatelyspaceda-long-the beam path ininterdigital;relationship such that a sinuouswaveene rgy path is formed'througlithe-device defined by the loading members, said loading members having apertures therein 'aligned-with'the beam path, and meanselectrically insulating saidffirst pluralityof loading members from;said second plurality, a source of electrical potentials m'eans forcoupling thefirst and second pluralities of members to s'aid sourcewhereby said first and second pluralitiesareatdifferent relativepotentials such 'tha't focusingelectrostatic fields extend betweenadjacent loading members at the beam path apertures, the dimension ofthe loading members inthe direction of thebeam path oi Qneplfirality ofloading. members being greater'than the ,dimension in :the direction ofthe beam path of] the loading members ofthe other plurality. i i

V 4,1A slow-wave electron beam device of the typewhere- ,in anelectromagnetic wave is made tq-travel through'the .dQYiCQ coupled toand sub V s t a y atith vi l i i' P a electron beam therein such that anenergy'exchange occurs ,betwe emthe beam and the wave comprisingmeansjfor p uc ng a be m pt e sct g sisl r q fi re-u h sa z c a s o -w e,st ta e t ma e w t 1. 6 l mr c mp i ing-a fir t plu a it 9. ,,lea inmembe ss ss tco n t p h ruan l assg a hers. ele trical y,cquulsdt fllq rthe membe s h 1 i interdigit l relatio sh p such. t a .v a" m Q J r ypathv orme th ought dqvis fls a ns Wi oadi amem e aid cai i ..-ms be shain apertures ,lec r cal poten a qf a ti Pluralities o ca ing memberslsuc a ha ett9$t focusing fields extend between adjacent loading membersat the beam path apertures.

5. A slow-wave electron beam device of the type wherein anelectromagnetic wave is made to travel through the device coupled to andsubstantially at the velocity of an electron beam therein such that anenergy exchange occurs between the beam and the wave comprising meansfor producing a beam of electrons, a base member having a plurality ofequally spaced loading members mounted thereon and extending inwardlyinto the device, a top plate positioned above said base member having aplurality of equally spaced loading members mounted thereon andextending toward the base member, said latter loading members being ininterdigital relationship with said former loading members such that asinuous wave-energy path is formed through the device defined by theloading members, said loading members each having an aperture therein,the apertures being aligned within the device so as to be aligned withthe electron beam path therethrough, the dimension in the direction ofthe beam path of each of said latter loading members being difierentfrom the like dimension of each of said former loading members, and

means for mounting said top plate on said base member includinginsulation electrically insulating the top plate from the base memberwhereby difierent direct current electrical potentials may be applied tosaid base and top plate such that electrostatic focusing fields extendbetween adjacent loading members at the beam path apertures.

References Cited in the file of this patent UNITED STATES PATENTS2,289,756 Clavier July 14, 1942 2,489,082 De Forest Nov. 22, 19492,545,595 Alvarez Mar. 20, 1951 2,645,738 Coeterier July 14, 19532,653,270 Kompfner Sept. 22, 1953 2,679,615 Bowie May 25, 1954 2,800,606Ping King Tien et a1 July 23, 1957 2,842,704 Van Iperen July 8, 19582,845,571 Kazan July 29, 1958 FOREIGN PATENTS 1,006,336 France J an. 23,1952 1,034,007 France Apr. 8, 1953

